OpenSpand announcement

[siggi]

A small BASIC and M/C program to relaunch the Spand back into overlay mode then launch ZXpand commander

Yes, but who wants to type in that "small BASIC and M/C" program again and again and again after having used the ZX81 rom?
ZxPand-Rom is not available, thus it's not posibble to save the "small BASIC and M/C" progam for later usage (exept using a cassette recorder )

Siggi

[Moggy]

Just include as it part of any program you are using and call it as needed, simple really I would have thought but then again judging by your past posts you have no time for Spand so not a problem for you.

[Mustermann]

I know a little about Minstrel 3.

It is using 2x 74HC257 for keyboard input. This part is not an open collector chip as the ZX81 ULA is. So external keyboards do not work without a modification.

I assume that OpenSpand will not be able to inject keystrokes as well.

Possible solution: Add 5 diodes at the output of the 74HC257 and some pull up resistors to those lines.
Minstrel 2 might be similar to that.

I implemented that at my minstrel but was not able to test an external keyboard yet.

Greetings from Mustermann

Just had a look to ZX81+38 schematic. 74HCT541 isn't an open collector as well.
Pull up resistors are already in place so 5 additional diodes will make it openspand ready.

[siggi]

Just include as it part of any program you are using and call it as needed ....

Instead of "patching" all programs, I had in one of my laptop-zeddies a simple (mechanical) switch to toggle between 2 roms at runtime.
But using a "poke" board (having a latch at rom address 8 or 9, like Kai did it in his ZX96 http://www.fischerkai.de/zxteam/zx96_e.htm) would be a solution, which could also be used by BASIC programs: http://www.fischerkai.de/zxteam/pokekart.gif
POKE 8, 2

Siggi

Addendum:
Example program

Code: Select all

10 REM enable ZX81 rom for printing
20 POKE 8,1
30 LLIST
40 REM enable ZxPand for saving
50 POKE 8,2
60 SAVE "example"

[nollkolltroll]

Just had a look to ZX81+38 schematic. 74HCT541 isn't an open collector as well.
Pull up resistors are already in place so 5 additional diodes will make it openspand ready.

Would you mind drawing a simple schematic of the solution? I've tried several different variants on my Minstrel 2 without success. I believe I understand what you are saying and how it should work, but I simply can't get it to work. The Minstrel 2 uses a 74LS365 just like the ZX80, but the solution should work the same with a '365 or a '541.

[1024MAK]

The point is that the output drivers (in the chip) for the outputs to the data bus need to be able to pull the value for the relevant data line low to logic zero but NOT drive it high to a logic one.

As the chips used have push-pull output stages, some extra circuitry is needed. For modifications to existing boards, this circuit is the most practical if doing it by hand:

The diode is preferably a BAT41, BAT42, BAT43, BAT 46, BAT48, BAT85 or similar. If you can’t get any of these, 1N4148 may work.
If the design already has pull-up resistors between each data bus line and the +5V rail, no further resistors should be needed. Otherwise you may need to add them. The value depends on the type/technology of the chips used. The given value of 2.2k is a comprise between speed and power.

Mark

[Mustermann]

That is roughly what I added to my Minstrel 3.

Depending on the design of OpenSpand it either need to be applied to all 8 data lines or only to those that are doing keyboard input.

If I understood right, Paul has an prototype of OpenSpand at hand. So we may test that with my Minstrel 3 in Helmarshausen in the begin of March.

[nollkolltroll]

Thank you Mustermann for the picture! Will try again tomorrow, I now know I missed the pull-ups. There were already pull-ups on the other side of the chip to fool my mind. Silly me.
Yes, Paul has both the first prototype revision and now the second as well, but I have not gotten any firmware running on it since I am waiting on a package from Paul. Me coding in the blind has not yielded a working board unfortunately, but I have very high hopes of getting it up and running quickly

[nollkolltroll]

And there will only be 5 diodes/resistors needed as the OpenSpand only tries to manipulate bits 0-4.

[1024MAK]

Thank you Mustermann for the picture!

Mark